I created this to for a garage door opener. I made it so when you take the lid off, you can get to all sides of the bottom without hindrance of sides being in the way. Likewise, I used 2-56 thread inserts in the standoffs and the sides to hold the lid on. It only needs one to hold the lid on, but I designed it, so you could put it in all sides. I supplied the FreeCAD files, so you can adjust as needed. 

2-56 thread inserts from McMaster-Carr - https://www.mcmaster.com/94459A240/

2-56 bolts from McMaster-Carr - https://www.mcmaster.com/91251A079/